The present invention is directed to an enossal implant which is also known as an endosteal or endosseous implant. The implant has a base structure which is snugly mounted in a bone of the jaw and has a threaded internal bore for receiving a spacer element which threadably receives a metal implant post of a fastening head and fastening means. The spacer element is provided with a centering collar which is engageable with a shoulder on an upper edge of the base structure and receives an intermediate element made from an elastic, plastic material which will concentrically surround the implant post.
U.S. Pat. No. 4,793,808, whose disclosure is incorporated by reference and which corresponds to European Published Application 0216 931, discloses an implant in which a spacer sleeve has a bore open at both ends and is made of a plastic material. An intermediate element is directly inserted in the basic structure and in conjunction with the spacer sleeve assumes responsibility for the cushioning of the fastening head or denture with respect to the basic structure in all directions. In other words, it acts for cushioning the forces created by both vertical and lateral acting loads. Simultaneously, an electrical insulation is insured between the denture and the basic structure to prevent the occurrence of harmful creeping currents which can lead to corrosion and irritation of the body tissue.
The known implants in principle have proven satisfactory, but it has been found that the intermediate element, which not only has a bearing and dampening function but also a fastening function for the implant post, has a fatigue breakage tendency, particularly under tension. It has also been found that the extent of the dampening should possibly be adjustable so that greater flexibility is available to allow a greater variety of uses for the device.